1. Field of the Invention
The present invention relates, in general, to an insulating adhesive tape for semiconductor chip packages and, more particularly, to an insulating adhesive tape with a coefficient of thermal expansion suitably designed to improve the reliability of lead-on-chip (LOC) type semiconductor chip packages based on copper lead frames.
2. Description of Related Art
As described in U.S. Pat. No. 4,943,843, LOC type semiconductor chip packages were suggested for packaging semiconductor chips at high densities. With reference to FIG. 1, there is a structure of a typical LOC type semiconductor chip package. Generally, in such a conventional LOC type semiconductor chip package structure, an insulating tape 1 is applied between a lead frame 2 and semiconductor chip 3 to bond them to each other. Another insulating tape known in the art has a tripartite structure consisting of a polyimide base film on either side of which a thermoplastic and a thermosetting adhesive layer is formed. U.S. Pat. No. 5,583,375 discloses a tripartite insulating tape comprising a base film 25 to 125 xcexcm thick with the adhesive layer ranging, in thickness, from 10 to 30 xcexcm.
Conventionally, LOC packages adopting nickel-based lead frames have been extensively used. However, copper lead frames are recently preferred because of high-speed signal transmission and thermal radiation of packages. When the insulating tape which has a base film with a thickness of 25-125 xcexcm and adhesive layers with a thickness of 10-30 xcexcm is used, semiconductor chips packaged on lead frames show good reliable results. In contrast to nickel lead frames, the semiconductor chip packages adopting copper lead frames do not ensure reliability in the operation of the chips when the insulating tape suggested in U.S. Pat. No. 5,583,375 is used.
Leading to the present invention, the intensive and thorough research on insulating tapes for use in semiconductor chip packages, conducted by the inventors, resulted in the finding that the coefficient of thermal expansion of an insulating tape plays an important role in determining the performance of the semiconductor chip packages adopting copper lead frames.
Therefore, it is an object of the present invention to overcome the above problems encountered in the prior art and to provide an insulating tape with such a suitable coefficient of thermal expansion to improve the reliability of LOC type semiconductor chip packages adopting copper lead frames.
Based on the present invention, the above object could be accomplished by a provision of an insulating tape for use in lead-on-chip type semiconductor chip packages having copper lead frames, which comprises a base film on either of which an adhesive layer is formed, and ranges in coefficient of thermal expansion from 16.0 to 23.5 ppm/xc2x0 C.